let a = 1;
let b = [1, null, "a"];
let c = { x: 1, y: "a" };

let d = (x = 1) => x + 1;

window.onkeydown = (event) => {
  // console.log(event.button);
  console.log(event.key);
};

// 类型断言
interface Foo {
  bar: number;
}
// let foo = {} as Foo
// let foo = <Foo>{}
let foo: Foo = {
  // 声明的时候指定类型
  bar: 1,
};
// foo.bar = 1
